A professional-grade Glute Ham Developer (GHD) machine used for core, posterior chain, and abdominal exercises like sit-ups and back extensions.
sit-ups on that GHB machine where you're going all the way down.
"
"The speaker refers to doing sit-ups on the 'GHB machine' (a common mispronunciation of GHD/Glute Ham Developer) where you go all the way down."